A scroll fluid machine comprises a housing, two fixed scrolls each of which is fixed on each side of the housing, an endless transmitting member connected to an electric motor, a driven pulley wound by the transmitting member, a thrust-offsetting shaft rotatably mounted at a position eccentric from a axis in the driven pulley, two orbiting scrolls each of which is fixed at each end of the thrust-offsetting shaft which rotates to form a compression chamber with the fixed scroll, and a self-rotation preventing device disposed between the housing and the orbiting scroll.